1. Field of Technology
The present invention relates to wireless transmission technology for effectively utilizing frequency bands to maximize transmission capacity in airplanes and other types of aircraft.
2. Description of Related Art
In-flight entertainment (“IFE”) systems used in passenger planes in recent years have helped make long-distance flights more enjoyable by providing passengers with in-flight entertainment services such as movies, audio programming, games, and even Internet browsing. The movies, audio programming, Internet data, and other information accessible by these systems are typically stored in an on-board server, and delivered from the server by coaxial cable, optical fiber, or other wired medium as either analog or digital transmissions. IFE equipment generally includes a ceiling-mounted projector and an LCD or other type of video monitor, as well as compact, individual monitors and controllers (handsets) installed at individual passenger seats.
The main transmission cable from the server is generally located in the ceiling, and other ceiling-mounted devices are connected by trunk lines from the main cable. In order to connect to devices located in the floor-mounted seats, large numbers of relay cables are wired through the side walls of the aircraft. Because maximizing the operating time of high cost airplanes is a major concern for airline companies, airlines frequently change the routes on which aircraft are used and the ticket class configuration of the planes. This necessitates changing the seat positions, which is preferably done in a short time and at low cost. However, because changing the seating configuration also means that the relay lines in the side walls must also be changed, changing the seating arrangement takes a long time and is thus expensive. There is, therefore, a need to change from a wired to a wireless transmission medium.
For years some aircraft have also been equipped with an aircraft telecommunications system enabling telephone communication with ground stations. To prevent RF interference with the ground telephone system, these on-board telecommunication systems are assigned a dedicated wireless frequency band that is reserved for in-flight telephone systems. Dedicating a wireless frequency band to such in-flight telephone systems, which have few subscribers and carry few calls, is an inefficient use of bandwidth, however, and technologies enabling sharing bandwidth with the ground telephone system without adversely affecting the existing phone system have been proposed.
When a mobile station installed in an aircraft selects a wireless frequency for communication but the selected wireless frequency is already being used for telecommunication with another mobile station and this communication is subject to noise caused by RF interference from the mobile station on the aircraft, reference patent 1 below teaches a method of unconditionally switching the wireless telephone frequency that is already in use to another RF frequency, and preventing that frequency from being used for telecommunication on the ground system if the selected RF communication frequency is not already being used. This technology enables economically deploying mobile communication systems enabling in-flight telephone services without setting aside new wireless frequencies reserved for in-flight telephone service and without requiring the installation of new dedicated equipment.
Reference patent 2 below teaches technology for controlling the transmission power of mobile in-flight telecommunication equipment to prevent RF interference interrupting car phone systems operating on the terrestrial telephone system, and controlling the reception power in order to prevent communication interference caused by RF interference from terrestrial car phone communications. This technology enables economically deploying mobile communication systems enabling in-flight telephone services without setting aside new wireless frequencies reserved for in-flight telephone service and without requiring the installation of new dedicated equipment.
Reference patent 1: Japanese Unexamined Patent Appl. Pub. H02-39736
Reference patent 2: Japanese Unexamined Patent Appl. Pub. H02-39739
Transmitting primarily video information to individual seats inside an aircraft requires significant bandwidth. If a broadcast system that transmits the same content simultaneously to each seat is used and the video signal is sent to each seat at a 5 megabit/second bit rate, the transmission path only requires the same 5 Mb/sec transmission capacity. However, if an on-demand unicast system enabling each user to receive content as desired is used, a transmission path with a capacity exceeding 1 Gb/second must be provided for each of several hundred seats. While the transmission load on the relay lines is not as great as the main trunk line, each relay line supplies anywhere from several to several ten seats and a transmission capacity of from several ten to several 100 megabits/second is therefore required.
Converting this wired system to a wireless system requires building a system that can assure a transmission capacity between several ten to several 100 megabits/second without adversely affecting the terrestrial wireless phone system. With the technologies taught in reference patents 1 and 2, however, the wireless telephone transmission capacity is less than or equal to 1 megabit/second, and the large transmission capacity noted above cannot be assured.